Cutting tool assemblies for such applications as mining or road milling typically comprise a cutting tool, sometimes referred to as a cutting pick, rotatably mounted within a support block. The support block in turn is mounted onto a drum or other body, typically by welding, which in turn is driven by a suitable drive means. When a number of such support blocks carrying cutting tools are mounted onto a drum, and the drum is driven, the cutting tools will engage and break up the material sought to be mined or removed. The general operation of such a mining or construction machine is well known in the art.
Various retaining devices have been proposed or used to mount a cutting tool, rotatably or otherwise, within a support block. For example, U.S. Pat. No. 4,505,058 to Peterson shows a retainer having two legs. This retainer is intended to be used with a support block having a recess with specially configured sidewalls which cooperate with the bends in the retainer legs to hold the retainer in place. More specifically, the sidewalls of the recess include projections to limit movement of the retainer with respect to the support block. This type of retainer is relatively difficult to move in order to disengage the retainer from the cutting tool in that a screwdriver or other similar object must be inserted into the recess and under the top of the retainer in order to pry and move the retainer. Like other similar retainers relying on prongs, the two legs of this retainer provide only four shear zones or areas where the retainer overlaps both the cutting tool and the support block. Because these shear zones prevent disengagement of the cutting tool from the support block, the number of such shear zones relates to the strength and durability of the retainer.
U.S. Pat. No. 4,883,129 to Lonn et al. shows another retaining device or ring which overlaps a cutting tool shank and a support block along substantially the entire length of the retaining ring. Consequently, the retaining ring provides a single, continuous shear zone along its entire length. However, this type of retaining ring is difficult to install and remove. More specifically, this retaining ring does not provide any slots or openings which may be grasped or which may receive a device for prying the retaining ring from the cutting tool shank. Furthermore, because the portion of the retaining ring that overlaps the support block is relatively narrow, this type of retaining ring does not sufficiently secure the cutting tool within the support block over an extended period of time.